Probability → Basics → Vocabulary → Probability Formula

The probability of an event can be calculated by the proportion (or probability) formula

or

For example, in the basic probability vocabulary page, the question was,

**Example**

A coin is tossed two times. What is the probability that both times the head was occurred?

**Answer**

Here, the sample space is

And, the favorable event, or an event for which we want to find probability is . This event is 1 among the total 4 events. Hence, and . The probability that both of the events are “heads” is thus

**EXAMPLE 2**

A fair dice is rolled once. What is the probability that an even number is occurred?

**Answer**

If a dice is rolled, any number from 1 to 6 can occur. So, the sample space is

And even numbers are three: 2,4,6. So favorable events () are 3, and total events () are 6. Hence,